This is a very large Yowah Nut Opal, mounted with a five-lead sixteen-bight 18K Champagne gold Turk's Head. I like the stones that are polished on both (or all) sides, as they are admirably suited to this sort of setting. If the stone is flipped over and lands on the other side, it is just as eye-catching, so it is simply a matter of personal preference which side is to be referred to as the "front".